The present invention relates to optical pumping of lasers, and in particular, to an optical element for homogenizing and concentrating the output of laser arrays used to pump solid-state lasers.
A high-average-power solid-state laser is typically pumped by injecting light from high-power two-dimensional semiconductor laser arrays. The arrays are also called stacks because they are stacks of bars. The laser arrays are frequently fitted with lenses that separately collimate the output of the bars so that the pump light is collimated well enough for transmission to the solid-state laser gain medium. The resulting output from a typical array consists of a beam of light from each bar with cross sectional dimensions of 1 mm by 1 cm. The spacing of the bars is typically about 1.8 mm, so the overall irradiance distribution from the array consists of bands of light that are separated from each other. Part of the power of the pump light is deposited as heat in the gain medium. Temperature non-uniformity of the gain medium causes wavefront distortion and depolarization of the laser light, which degrades the quality of the solid-state laser beam. It would be advantageous if the individual beams from the bars could be made to overlap or to partially overlap in the gain medium to thereby homogenize the pump beam.